静态html
<div id="app" style="color: #FF3640;">
  Hello HTML
</div>
<style>
  #app {
    font-style: italic;
  }
</style>

<hr>
js 控制
<div id="app-2">
</div>

<hr>
jquery 控制
<div id="app-3">
</div>

<script>
  // document.findDocumentById('app-2').innerHtml = "Hello World"
  document.getElementById('app-2').innerHTML = 'Hello JS'
  setTimeout(function() {
    document.getElementById('app-2').innerText = '哈哈😀😀😀!'
  }, 3000)
</script>

<script src="https://code.jquery.com/jquery-3.5.1.min.js"></script>
<script>
  $('#app-3').html('Hello JQuery')
  setTimeout(function() {
    $('#app-3').text('😀😀')
  }, 4000)
</script>
